Method of producing textured surfaces on medical implants

ABSTRACT

Methods of texturizing medical implants are provided which involve embossing the surface of these implants to create a textured pattern. Preferred roll embossing techniques are disclosed for improving scratch resistant properties, minimizing glare, improving lubricant retention and/or creating random or uniform patterns on medical implants, such as the outer shield of pacemakers and defibrillators, as well as orthopedic implants.

FIELD OF THE INVENTION

[0001] This invention relates to a method of embossing strip materialused for medical implants, and more particularly, to methods ofproducing textured surfaces on implant quality titanium strip.

BACKGROUND OF THE INVENTION

[0002] Medical implant applications, such as implantable pacemakers,defibrillators, drug infusion pumping devices, and orthopedic implants,are commonly made from, or housed within, corrosion-resistant metal,such as titanium, titanium alloys, nickel alloys or stainless steel.

[0003] Medical implants have often been finished by a variety oftechniques, including hand polishing, media blasting, and electrolyticand chemical polishing. It is difficult to effectively polish allsurfaces of medical implants, since they often have small features andintricately curved surfaces. Additionally, mechanical and electrolyticpolishing can produce a surface finish that is bright and lightreflective. Such a surface can sometimes lead to glare under the brightlight of a surgical procedure, and reveal scratches and blemishes whichare, at a minimum, aesthetically undesirable, and which can sometimeslead to a part's rejection on purely cosmetic grounds.

[0004] Matte or “scratch resistant” surfaces have been produced bychemical polishing and media blasting techniques. Such surfaces are indemand, since they are less light-reflective and conceal scratches andblemishes, rather than literally resisting them as the term “scratchresistant” suggests.

[0005] Recent artisans have attempted to create matte surfaces onmedical implants. Baswell et al., U.S. Pat. No. 4,704,126, issued Nov.3, 1987, discloses a method of chemically polishing medical implants byimmersing them in a mixed acid solution to produce a smooth, mattesurface. This acid polishing technique is principally designed tominimize tissue fixation on titanium or titanium alloy medical implants,while preventing reflective glare from interfering with surgicalprocedures. While smoothing the exterior of medical implants offers someadvantages, such surfaces do not conceal scratches and blemishes wellenough, and are not known to retain metal working lubricants in anysignificant way during metal working processes, which is a disadvantagein deep drawing metal working operations. In addition, acid bathsgenerate a considerable amount of hazardous waste, and require timeconsuming cleaning, washing and acid neutralization steps in themanufacture of medical implants.

[0006] Johnson, U.S. Pat. No. 5,673,473, issued Oct. 7, 1997, describeda method of creating a scratch resistant surface on a medical implantshield, by blasting the titanium metal strip precursor with metallicmedia. The '473 patent reports that metallic media blasting enhancesscratch resistant properties, while simultaneously improvingmanufacturing “throughput” without sacrificing shield biocompatability.Despite the teachings of this patent, metallic media blasting alwayspresents a chance that embedded media will unintentionally be retainedon the implant surface. Media blasting generally forms the same textureon all surfaces of the metal strip and is a relatively slow operation toperform. Media blasting is also incapable of controlling the nature ofthe texture, such as the degree of roughness, randomness or orientation.

[0007] Accordingly, there remains a need for providing textured surfaceson implant quality metal strips which improves manufacturing“throughput”, produces a high quality scratch resistant surface, andimproves control over the nature of the texture imparted onto themedical implant surface.

SUMMARY OF THE INVENTION

[0008] In a first embodiment, the present invention provides a method ofmanufacturing an outer shield of a medical implant, which includesproviding a sheet metal substrate having first and second planarsurfaces thereon. The method further includes embossing the sheet metalsubstrate to provide an embossed sheet metal substrate having a texturedpattern on at least the first surface, and forming the embossed sheetmetal substrate into an outer shield exhibiting said textured pattern onat least an external facing surface portion for helping to conceal smallsurface defects thereon.

[0009] The present invention provides surface defect concealment onmedical implants, and especially outer shields of pacemakers anddefibrillators, and other implantable devices. The embossing processesof this invention are more expedient than media blasting or chemicalpolishing. For example, the embossing step of this invention can providea textured surface on a medical grade titanium strip at speeds of ten tofifty times faster than media blasting. Since no particulate media isused in the preferred embossing steps to form the surface texture, thereis virtually no chance of embedding media or foreign objects in thesurface of the implant. While media blasting forms an identical textureon either side of the strip, the embossing processes of this inventionallow for differing textures on different locations on the strip byutilizing, for example, upper and lower rolls with different engravingpatterns. Additionally, while media blasting is, by its very nature, arandom process generating a random texture, the embossing processes ofthis invention can generate either a random, regular, periodic, orsemi-periodic pattern on the strip, as desired. Patterns simulatingwood, tweed, leather, and stuccos, can be engraved on titanium, titaniumalloy, nickel alloy and stainless steel metal strips, as desired. Morepreferably, a non-directional, non-reflective surface texture whichmimics media blasting, is used. Finally, no hazardous waste is generatedby embossing, since no acid baths are required. The textured surfacesproduced on the metal surfaces of this invention conform merely to theengraved tool design and the degree of pressure selected.

[0010] In further embodiments of this invention, medical implants areprovided having embossed textured patterns which retain lubricants tominimize galling in subsequent metal forming operations. Medicalimplants with textured embossed surfaces are also provided which havedifferent engraving patterns on their surfaces. For example, a simulatedleather grain can be produced on the exterior of the shield, with astucco-like pattern on the interior of the shield, so as to readilydistinguish these surfaces during subsequent manufacturing operation.Additionally, the embossed patterns of this invention can be designed toenhance tissue implantation on the surface of the medical implant, whendesirable, such as in bone ingrowth applications of orthopedic implants.Patterns can be developed which retain more or less metal workinglubricant, such as oil or detergent-based lubricants, for deep drawing,stamping or shaping operations.

BRIEF DESCRIPTIONS OF THE DRAWINGS

[0011] The accompanying drawings illustrate preferred embodiments of theinvention, as well as other information pertinent to the disclosure, inwhich:

[0012]FIG. 1: is a flow diagram of a preferred manufacturing method forproducing an outer shield of a medical implant;

[0013]FIG. 2: is a flow diagram of an alternative manufacturing methodfor producing an outer shield of a medical implant;

[0014]FIG. 3: is a front perspective view of a roll embossing machine inthe process of engraving a metal strip;

[0015]FIG. 4: is a top planar view of a bottom hardened steel engravingroll embodiment of this invention.

DETAILED DESCRIPTION OF THE INVENTION

[0016] This invention provides improved metal finishing techniques forproducing textured surfaces on medical implants, such as for example,the outer shield of pacemakers and defibrillators. This invention isalso applicable to shields or cases for implantable medicationdispensing devices, or the surface of orthopedic implants, stents,plates, orthopedic screws and any number of medical devices used incontact with the human body. As used herein, the following terms aredefined:

[0017] “Sheet or strip metal” means a substantially planar thin gaugemetallic substrate having a thickness of less than about {fraction(3/16)}″ (4.76 mm) inches;

[0018] “Roll embossing” means a three-dimensional texturizing processinvolving one or more engraved rolls.

[0019] “Embossing” means any method useful in providing a pattern orshape to a metal sheet material, including one-sided embossing(coining), roll forming of deep ridges (corrugation) and rotary or rollembossing.

[0020] With reference to the figures, and in particular FIGS. 1 and 2thereof, there is shown a pair of manufacturing sequences 100 and 200for texturing the implant quality metal strips of this invention. Whilethese preferred steps can be used in a different order, the disclosedsequence embodiments 100 and 200, provide a favorable combination oftexture and metal properties.

[0021] Sequence 100 begins with a source of strip metal, such as a coldrolled coil of titanium, titanium alloy, nickle, nickel alloy orstainless steel. Titanium and its alloys are often used in corrosiveenvironments, as in contact with body fluid, such as blood. Titanium hasa light weight, high strength-to-weight ratio, and non-magneticproperties. Depending on the predominate phase or phases in themicrostructure, titanium alloys are categorized as alpha, alpha-beta,and beta. This natural grouping not only reflects basic titaniumproduction metallurgy, but also indicates general properties peculiar toeach type. Chemically pure (“CP”) titanium and Ti-6Al-4V alloys arecommonly selected for medical implant applications, since they areextremely biocompatable materials. While CP titanium may contain smallamounts (<1 wt %) of O₂ or iron, it is an alpha alloy type having acoefficient of thermal expansion of 5.4×10⁻⁶ in/in-° F., within therange of 32-1000° F., and a tensile modulus of elasticity of about14.9×10⁶ psi. Ti-6Al-4V is an alpha-beta alloy type, having acoefficient of thermal expansion of about 3.9×10⁶ in/in-° F. over thesame temperature range, and a tensile modulus of elasticity of about16.5×10⁶ psi. CP titanium has excellent corrosion resistance andexcellent ductility for maximum formability during the drawing ofmedical implant shields. Ti-6Al-4V is one of the more versatile titaniumalloys, and is used in many corrosion resistant applications. It hasmuch greater electrical resistivity, having a RT electrical resistivityof 171 micro-ohms-cm, whereby the high purity titanium has a RTelectrical resistivity of 56 micro-ohms-cm. Other titanium alloys thatare useful for this invention include Ti-15Mo-2.7Nb-3Al-0.2Si, beta-21Salloy, which is an ideal candidate for orthopedic implants, due to itsextremely low hydrogen uptake efficiency levels. Like stainless steel,which is also a candidate for this invention, titanium sheet workhardens significantly during forming, even during media blasting andembossing. Minimum bend-radius rules are nearly the same for both,although spring back is greater for titanium. CP grades of heavytitanium plate are cold formed or, for more severe shapes, warm formedat temperatures of about 800° F. Alloy grades can be formed attemperatures as high as 1400° F. in inert gas atmospheres.

[0022] Despite their high strength, some alloys of titanium havesuperplastic characteristics in the range of 1500-1700° F. The alloyused for most superplastically formed parts is the standard Ti-6Al-4Valloy.

[0023] Selected titanium alloys useful in the methods of this inventionare disclosed below in Table I. TABLE I Titanium alloys propertiesTensile Coef. of thermal RT Yield Strength Modulus expansion RT ThermalElectrical Nominal alloy (10³) Minimum of Elasticity (32-1,000° F.)conductivity resistivity composition at room temp. (10⁶ psi) (10⁻⁶in./in.-° F.) (Btu-ft/h-ft²-° F.) (μohm-cm) *Ti (high 25 14.9 5.4 9.0 56purity)(Alpha) *Ti (plus 70 15.1 5.4 9.8 60 O₂,F)(Alpha) Ti-0.2Pd 4014.9 5.4 9.5 56 (Alpha) Ti-5A1-2.5Sn 115 16.0 5.3 4.5 157 (Alpha)Ti-6A1-2Sn- 4Zr-2Mo 120 18.5 5.6 — 199 (Alpha) Ti-6A1-4V 120 16.5 3.93.9 171 (Alpha-beta) †Ti-6A1- 4VEL1 120 16.5 5.6 4.2 171 (Alpha-beta)Ti-3A1-SV- 6Cr-4Zr-4Mo 160 15.0 5.4 — — (Beta) Ti-15Mo-3Nb- 3A1-O.2Si160 15.5 4.9 4.4 135 (Beta)

[0024] In the preferred manufacturing sequences 100 and 200, cold rolledcoil of titanium, titanium alloy, nickel, nickel-alloy or stainlesssteel is provided at cold rolled coil step 10. The strip within the coilshould be pre-rolled to a thickness of about 0.005-0.040 in, preferablyabout 0.010-0.020 in, with a target thickness of about 0.012 in. Thestrip material within the coil is used generally, especially in themanufacture of implantable medical device shields, due to its highstrength, ductility, fracture resistance, biocompatability and corrosionresistance. However, if the manufacturing methods of this invention areused with thicker substrates, such as for medical implants, the rollembossing techniques of this invention can be provided with larger nipspacing to enable larger materials to be texturized.

[0025] In the manufacturing sequence 100 of FIG. 1, the cold roll stripis embossed at roll embossing step 30. While it is anticipated thatother embossing technique could be useful for certain end-usesassociated with this invention, such as single-sided embossing(coining), for thicker substrates, roll forming for deep ridges, foradded strength, roll embossing is the preferred technique for medicaldevice shields. Ideally, the embossing machine 300 shown in FIG. 3 issituated directly after an uncoiler in the processing line and may befollowed by a number of different operations. Typically, theseoperations include recoiling, slitting or cutting-to-width, slitting,roll forming, stamping, or any combination thereof.

[0026] The preferred embossing machine 300 can either be a stationaryfixture in the metal processing line, or it can be made movable withwheels, rails, or a crane and lifting bolt assembly. While most machinesare driven with an integral motor and drive package, embossing can alsobe performed using the power of a recoiler or other device and anunpowered pull-through embossing stand. Horsepower requirements dependon line speed and, to a lesser degree, material thickness, pattern, androll size.

[0027] Located within the embossing stand of the preferred embodimentare two engraved and mated hardened steel rolls 320 and 330, gearedtogether to maintain top-to-bottom pattern registration. The engravedmetal embossing rolls 320 and 330 are preferably manufactured from highquality 52100 modified steel forgings, through hardened to 62-65Rockwell C. While this may take a little more time and be slightlyhigher in cost, it yields dividends in increased longevity and wear. Thewidth and diameter of these rolls 320 and 330 depends on the stripwidth, material thickness, pattern depth, and material tensile strengthand hardness.

[0028] In FIG. 4 a preferred embossing roll 330 is shown withprotuberances 340 and flat regions 335. While not presently committed toany particular pattern, leaving flat areas in the engraved roll canpreserve the original sheet thickness in certain areas to maintain fullmechanical strength. One or both rolls 320 and 330 can be engraved witha common or different pattern.

[0029] The engraved roll journals are housed in a bearing and blockassembly (not shown). In most machines, the upper roll blocks arestationary, while the bottom roll blocks are movable. The pressure withwhich the bottom roll is raised is referred to as the tonnage capacity.This figure also depends on the aforementioned parameters.

[0030] Embossing machines are generally sized to give 2″ of stripclearance on each side of an engraved embossing roll. However, each unitis custom-manufactured, so there are no standard widths. In fact,machines less than 6″ wide and more than 76″ wide are currently inoperation.

[0031] The reasons for employing embossed metal for medical devices canbe divided into two distinct categories: aesthetic and functional. Manyapplications serve both purposes.

[0032] Aesthetic uses of embossing are those which enhance theappearance of a product, such as the elimination of glare. By creating aseries of small peaks and valleys on the implant's shield, small surfacedefects, such as scratches and blemishes can also be more effectivelyconcealed.

[0033] The embossed medical implant applications of this invention thatbegin as aesthetic, such as scratch concealment, could very well end upwith functional improvements. Functional applications of embossinginclude those in which a performance characteristic is enhanced, and caninvolve, for example, better liquid dispersion and greater friction andstatic reduction, as in better metalworking lubricant retention duringdrawing and other metal forming operations. Deep textures on the outsideof the shield can also increase thermal conductivity by increasing thesurface area. Additionally, texturing the exterior can encourage tissueattachment. Embossed patterns can also improve stiffness and rigiditywhich improves the shield's toughness, stiffness and impact strength.

[0034] One additional benefit of increased stiffness is the ability toreduce weight and material to save on material costs. Reduction of “oilcanning”, diffusion of light, and decreased manufacturing rejects areother important side benefits.

[0035] The most popular embossed metal patterns include leather grains,wood grains, and stuccos, although almost any pattern can be engraved onthe mated set of hardened rolls 320 and 330. In the preferred implantsof this invention, a non-directional, non-reflective surface texture isused. Warnings, brand names, installation directions and otherinstructions can also become a part of the pattern. Creating a newpattern and engraving the rolls are complex and highly skilled tasks.Engravers can take any idea, prototype, or artwork and develop originaltooling by methods including electroforming, etching, punching, routing,laser, or computer generated graphic enhancement.

[0036] Once tooling has been manufactured, a mill is produced specificto the work roll that will be engraved. This mill displaces anacid-resist coating on the rolls and exposes metal, which issubsequently etched with acid and removed. The entire process isrepeated again and again until the full depth (usually about 0.001-0.1inch) and finish are obtained.

[0037] Thus, the pattern on the small mill is transferred to a largehardened work roll. This hardened top roll is then mated with and gearedwith a bottom roll in the embossing machine. Rolls can be re-engravedon-site as long as the pattern fidelity of the rolls and gear clearanceand roll diameter parameters remain adequate.

[0038] Three preferred methods for obtaining embossed metal strip forthe outer shields of this invention include:

[0039] 1. Purchase pre-embossed material from a service center, coilcoater, or custom embosser;

[0040] 2. Obtain a set of embossing rolls to be run in a third-party'sembossing machine for toll embossing applications; and

[0041] 3. Procure an embossing machine and roll set for in-houseproduction.

[0042] In any of these cases, one can compare the additional cost ofoutside embossing with the equipment and labor costs associated withinside embossing.

[0043] While embossed metal is handled and formed in exactly the sameway as its flat counterpart, several conditions are important to keep inmind.

[0044] Bending radii and die clearances must take into account thematerial's actual cross-section thickness versus material thicknessonly. Some deep draws or severe bends may distort, wash out, or evensplit open sharp patterns and should, therefore, be avoided (or testedon a small scale before production).

[0045] Shallower embossed patterns, preferred by this invention, such asthe leather grain family, may affect material flatness and, therefore,need corrective leveling. This is especially true as the productincreases in width.

[0046] A matched set of embossing rolls will deflect during theembossing process. While this deflection can be compensated for byadding crown to the rolls, this crown is pertinent to one particulargauge (usually the most commonly run). Embossing above or below thetarget thickness may result in sheet shape and/or pattern appearanceanomalies. Again, this is more pronounced with shallower patterns.

[0047] While materials more than 0.040 inch thick can be textured byroll embossing techniques, the result is usually a coined/embossedhybrid. This invention recommends staying with the 0.005-0.040 inchstrip thickness range for roll embossing, preferably about 0.010-0.020inches, with a target thickness of 0.012 inches. Uniform in-feed tensionis desirable while material can exit with or without tension.

[0048] In the next step 15, the strip 310 is treated to an alkalinecleaning step 15, prior to an annealing step 20. The alkaline cleaningstep 15 removes organic contaminates, such as oil, which reside on thesurface of the cold roll coil 10 from forming and handling.

[0049] The annealing step 20 is designed to stress relieve the sheetmaterial prior to subsequent processing. It is typically carried out ina vacuum or inert gas atmosphere, such as argon. While the annealingtemperature and sequence depends upon the type of alloy used, generallyfor titanium alloys, a temperature of about 1400-1800° F., preferablysolution treated at 1750° F., followed by a water quench or air cool, isacceptable. Titanium alloys can also be aged for up to 4-6 hours at1000° F.

[0050] In addition to the annealing step 20, a pickling step 25 isoptionally employed to remove the oxide layer formed during theannealing step, and also to clean the substrate surface withoutdissolving away the surface layer produced during the cold rolling ofthe coil 10. Following pickling 25, the strip is slit to final width atslit step 35, and is then sent to a subsequent forming step 40 (usuallyan intermediate manufacturer) for final manufacture into a medicalimplant shield, for example.

[0051] Sizing and fitting can also be accomplished after forming forproducing the final elements of the medical device shield itself. Sizingand trimming affects subsequent medical device manufacturing processes,such as machining and welding operations.

[0052] The forming step 40 of conventional medical device shields, suchas cardiac pacemakers, for example, operates by mounting one or moretextured strips in accordance with conventional methods. Initially, thestrip is used as a blank cut from the coil or strip of embossed titaniumsheet. A drawing punch (not shown) forces the blank holder through acylindrical opening in a dye, such that a half shield is formed from theflat blank. After trimming, this half-shield is mated with anotherhalf-shield. The finished medical device can be provided by enclosingthe internal electronics and battery cell into the shield halves. Thecircuitry then can be connected to the feedthroughs. Subsequent electronbeam (E B), laser or ultrasonic welding of the shield halves togetheralong their edges forms a substantially hermetic closure. A moldedplastic connector block assembly containing electrical connecters forattachment to the feedthroughs is typically installed as a final step.

[0053] In the alternative manufacturing sequence 200, shown in FIG. 2,the roll embossing step 30 is moved further down the processing line,after the optional pickling step 25. This provides the additionalbenefit of being able to emboss the sheet metal after it is softened bythe annealing step 20, which may require less tonnage, and may providegreater detail with less effort to print. Since a formed shield, forexample, will likely be further annealed prior to final assembly, movingthe roll embossing step 30 further on down the manufacturing line, willnot lead to a wasted annealing step.

[0054] From the foregoing, it can be realized that this inventionprovides improved methods for manufacturing medical implants havingtextured surfaces, and more particularly, to outer shields of pacemakersand defibrillators, having a scratch resistant surface manufactured in afraction of the time currently required by media blasting techniques. Itis further possible that roll embossing will provide shield metal thathas been strengthened by the textured surface formed to its surface.Additionally, the roll embossing, or other embossing, techniques of thisinvention can produce designed patterns for increased metal workinglubricant retention, decreased glare, and increased thermal conductivityfor suitable end-use applications. It is conceivable that the texturingdesigns of this invention can be combined with more conventional mediablasting, chemical, hand or electrolytic polishing to provide surfaceshaving multiple characteristics and properties on the same implant.Also, the embossing techniques of this invention do not contribute tothe contamination of the surface of the implant, and can be performeddirectly on the metal strip, without significantly changing its planarshape. Although various embodiments have been illustrated, this is forthe purpose of describing, but not limiting the invention. Variousmodifications, which will become apparent to one skilled in the art, arewithin the scope of this invention.

What is claimed:
 1. A method of manufacturing an outer shield of a medical implant comprising: (a) providing a sheet metal substrate having first and second planar surfaces thereon; (b) embossing said sheet metal substrate to provide an embossed textured pattern on said first planar surface; and (c) forming the embossed sheet metal substrate into an outer shield of said medical implant, said outer shield having an inside and outside surface, whereby said embossed textured pattern is located at least on said outside surface for helping to conceal small surface defects thereon.
 2. The method of claim 1 wherein said sheet metal substrate comprises a metal selected from the group containing titanium, nickle, and alloys thereof, and stainless steel.
 3. The method of claim 1 wherein said sheet metal substrate comprises cold rolled titanium or titanium alloy coil.
 4. The method of claim 3 wherein said titanium or titanium alloy coil is provided in a thickness of about 0.005-0.04 inches.
 5. The method of claim 1 wherein said textured pattern comprises a leather grain, wood grain, stucco grain or a combination thereof.
 6. The method of claim 1 wherein said textured pattern comprises a non-directional, non-reflective surface texture.
 7. A method of manufacturing an outer shield of a medical implant comprising: (a) providing a sheet metal substrate having first and second planar surfaces thereon; (b) embossing said sheet metal substrate to provide a textured pattern on said first surface; (c) cleaning said sheet metal substrate with an alkaline solution; (d) annealing said sheet metal substrate at an elevated temperature; and (e) forming the embossed sheet metal substrate into an outer shield of a medical implant having an inside and outside surface, whereby said textured pattern is located on at least said outside surface for helping to conceal small surface defects thereon.
 8. The method of claim 7 further comprising pickling said sheet metal substrate.
 9. The method of claim 7 whereby said sheet metal substrate is slit to final width prior to said forming step (e).
 10. A method of manufacturing an outer shield of a medical implant comprising: (a) providing a sheet metal substrate having first and second planar surfaces thereon; (b) cleaning said sheet metal substrate with an alkaline solution; (c) annealing said cleaned sheet metal substrate at an elevated temperature; (d) embossing said cleaned and annealed sheet metal substrate to provide an embossed surface thereon having a textured pattern; and (e) forming the embossed sheet metal substrate into an outer shield which exposes said textured pattern to help conceal small surface defects thereon.
 11. The method of claim 10 wherein said sheet metal comprises titanium or titanium alloy having a thickness of about 0.005-0.04 inches.
 12. The method of claim 10 wherein said annealing step (c) achieves a temperature of about 1400-1800° F.
 13. The method of claim 12 wherein said annealing step (c) is followed by a water quench or air cool.
 14. The method of claim 10 wherein said medical implant comprises a cardiac pacemaker or defibrillator.
 15. An outer shield for a medical implant comprising a sheet metal substrate having first and second surfaces thereon; said first surface including an embossed, textured pattern having a non-reflective appearance for helping to conceal small surface defects on said implant.
 16. The outer shield of claim 15 wherein said medical implant comprises a pacemaker or defibrillator;
 17. The outer shield of claim 15 wherein said sheet metal substrate comprises stainless steel, or nickel, titanium, or alloys thereof.
 18. The outer shield of claim 15 having a thickness of less than about {fraction (3/16)} inches (4.76 mm).
 19. A medical implant comprising the outer shield of claim
 15. 20. A method of manufacturing an outer shield of a medical implant comprising: (a) providing a sheet metal substrate comprising titanium having first and second planar surfaces thereon; (b) cleaning said sheet metal substrate in an alkaline solution; (c) annealing said sheet metal substrate at an elevated temperature; (d) embossing said sheet metal substrate to provide an embossed textured pattern thereon; said embossing step being provided either before said alkaline cleaning step or thereafter; and (e) forming the embossed sheet metal substrate into an outer shield having an inside and outside surface whereby said textured pattern is located on at least said outside surface for helping to conceal small surface defects thereon. 